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# Synthesis and characterisation of novel metal pyrophosphates

Baker, Annabelle R. (2014)
Ph.D. thesis, University of Birmingham.

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## Abstract

This thesis describes the synthesis, properties and structural characterisation of Mg$$^2$$$$^+$$, Mn$$^2$$$$^+$$and Ti$$^4$$$$^+$$ pyrophosphates and Li and V substituted analogues.
α and β polymorphs of MgH$$_2$$P$$_2$$O$$_7$$, were isolated by a novel acid melt synthetic route. Both polymorphs crystallised in monoclinic space groups, with α-MgH$$_2$$P$$_2$$O$$_7$$ isostructural with NiH$$_2$$P$$_2$$O$$_7$$ and β-MgH$$_2$$P$$_2$$O$$_7$$ isostructural with CaH$$_2$$P$$_2$$O$$_7$$. Rietveld refinements of NPD data gave excellent fits to both structural models. MgLi$$_0$$$$_.$$$$_8$$H$$_1$$$$_.$$$$_2$$P$$_2$$O$$_7$$was also isolated with Rietveld refinement suggesting two similar possible structural models.
MnH$$_2$$P$$_2$$O$$_7$$, a structural polymorph of β-MgH$$_2$$P$$_2$$O$$_7$$ was also synthesised via a similar route. Magnetic analysis revealed MnH$$_2$$P$$_2$$O$$_7$$ to be paramagnetic, with a small antiferromagnetic component. Incorporation of Li was again achieved via the addition of lithium carbonate during synthesis. Rietveld refinement of NPD data suggests a similar structure to that of MnH$$_2$$P$$_2$$O$$_7$$ and a composition of MnLi$$_0$$$$_.$$$$_5$$H$$_1$$$$_.$$$$_5$$P$$_2$$O$$_7$$.
A metastable polymorph of TiP2O7 has been successfully synthesised at low temperature and adopts a structure similar to the ideal cubic structure. Incorporation of vanadium resulted in an expansion of the unit cell. Both phases undergo a phase transition above 275°C to the ideal cubic structure. Addition of vanadium results in an unusual uniform spherical morphology unseen in parent phase.

Type of Work: Ph.D. thesis. Wright, Adrian Colleges (2008 onwards) > College of Engineering & Physical Sciences School of Chemistry QD Chemistry University of Birmingham 5524
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